THE CIRCULATION OF THE BLOOD. 199 



By placing three small India-rubber air-bags or cardiac sounds in the 

 interior respectively of the right auricle and the right ventricle, and in 

 an intercostal space in front of the heart of living animals (horse), and 

 placing these bags, by means of long, narrow tubes, in communication 

 with three levers, arranged one over the other in connection with a reg- 



Fig. 168. Apparatus of MM. Chauveau and Marey for estimating the variations of endocardial 

 pressure, and production of impulse of the heart. 



istering apparatus (fig. 168), Chauveau and Marey have been able to re- 

 cord and measure with much accuracy the variations of the endocardial 

 pressure and the comparative duration of the contractions of the auricles 

 and ventricles. By means of the same apparatus, the synchronism of 

 the impulse with the contraction of the ventricles, is also well shown; 

 and the causes of the several vibrations of which it is really composed, 

 have been demonstrated. 



In the tracing (fig. 169), the intervals between the vertical lines rep- 

 resent periods of a tenth of a second. The parts on which any given 

 vertical line falls represent simultaneous events. It will be seen that 

 the contraction of the auricle, indicated by the marked curve at A in 

 first tracing, causes a slight increase of pressure in the ventricle which 

 is shown at A' in the second tracing, and produces also a slight impulse, 

 which is indicated by A* in the third tracing. The closure of the semi- 

 lunar valves causes a momentarily increased pressure in the ventricle at 

 D', affects the pressure in the auricle D, and is also shown in the tracing 

 of the impulse D". 



The large curve of the ventricular and the impulse tracings, between 

 A ; and D', and A* and D", are caused by the ventricular contraction, while 

 the smaller undulations, between B and c, B' and c', B* and c*, are 

 caused by the vibrations consequent on the tightening and closure of 

 the auriculo-ventricular valves. 



It seems by no means certain that Marey 's curves properly represent 

 the variations in intraventricular pressure. Much objection has been 



